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Sure

But if you had actually tried to see what I was getting at is that such a small increase isnt gonna make a noticeable difference. Going from a 46mm to a 47mm valve wont significantly affect the valve opening area. Its only a 2.2% increase in valve size, which reflects proportionally on the valve opening area. Especially when there is a hotter cam and higher compression in the same motor, its foolish to think the slightly upsized intake valve was a factor. I dont think its necessary for everyone to be lusting after the 3.5 head when its really not much different. Misinformation is a bad thing.

For now

Its just that every other bit of info I've ever seen has said otherwise, and I've seen so many errors in the ETK its not good for much. I'd be a sucker if I just believed some dude on a message board. That'll screw you up.

Re: Sure

Misinformation is a bad thing.
sure is as in a 47mm valve is 0.73 cm2 larger. A 46mm vlave is has a area of 16.62 cm2 and a 47mm valve has a area of 17.35 cm2. So its aprox 4.4% bigger not 2.2. Just worked out were our local BMW dealer stealership gets its creative acounting from..............

Re: The math says:

Why are we talking cubic mm ? when valve size only increases mm2. Cubic valve flow rates need to take into account cam lift as well to get a cubic mm comparison. optimum valve lift increases with valve size. The main thing you have missed is that the longer duration of cam the more prononced the power band is, so for a road car ther is only so much duration you can have and still alow the engine to tick over. So valve size on a road engine is very important as it alows better breathing with out using wild cam duration, and becomes more important as you tune a road engine with out lossing drivability.You have also not taken into account imishion co2 levels, the longer the cam duration the dirtyer the engine runs. So just going for a `hoter` cam would not be the answer, especialy for the American market.
If all you needed to due was use motronic and a hotter cam do you think BMW would have botherd with a 24 valve head ?? I`m currently getting 290 bhp out of a modified m30 3.5 with a 12 valve head but there is no way it would pass a imishion test, but as its going into a car that dosnt need to be co2 tested for the MOT it dosnt matter.
The bottom line is that BMW could not get the required power out of the small valve head and still pass imishion standrds, have good drivability and good fuel consumption.
count (or cant count) you seen to be looking for a very simple answer to a very complicated question but in fact the answer is a lot more complicated than cam and valve size v`s bhp. Infact motronic didnt do that much for the cars power but more for the engines imishion control and fuel efficency. some one also in a previouse thread stated that motronic increased the spark advance do to higher compreshion ratios, this is not the case. The higher the compreshion ratio the more retard you need to stop pinging, or a higher octane fuel. So what tends to happen is the unless you use a higher octane fuel any car with a lamba probe or knock sensers retards the ignition the higher the compreshion ratio, the more retard you get the less power the engine gets.
so to recap, you cant just increase cam duration or compreshion ratio`s to increase power and pass imishion (smog) tests on a mass production engine.There comes a point with cam duration were the engine has a power band high up the rev range and will no longer idle reliable. With compreshion ratios you get to a point were you can no longer run regular pump gas but need higher octane fuel to stop detanation (pining,pinking as we call it in the uk)and alow the engine to run with as much ignition advance as posible, thus generationg high HP. One thing you can do is increase the volume of the engine and increase the valve size. Every thing is a compramise between power,eficancy,drivability, reliabilty.
you cant beat CC`s for reliable power

Re: Sure

The area of the circular face of a tappet valve is not a good indicator of flow. "Curtain area" is a better measure and is typically approximated by the circumference of the valve seat or valve head times the valve lift. Since enlarging a 47mm diameter valve by 1mm will increase the valve's circumference by about 2%, it will increase flow by about 2%.

Re: Sure

on a flow rig in real terms we found a increase of 5.8% going from a 47mm to 48mm (using a 48mm valve seat) and a 3.4% increase going from 48m to 49mm (using a re-cut 48mm seat).Those figures were after porting to suit. With a bore of 93.8 mm 49mm was the largest valve we were able to fit and still have room left for a 40mm exhaust valve.

Thats all nice and good, but

thats all just your opinion. Doesnt mean much. I still say that its not a good reason to get all wet all over yourself for a 3.5 head, as 1mm more on the intake side is not going to make a noticeable difference. Unless theres some magic [Oops!] going on here, and a 2% increase in valve size gets a 16% power increase, its the cam and CR that do it, mainly the cam. I'm going to say your m30 is turbocharged. And its emissions, only one "i". I can only trust your two cents so much with spelling like that.

Re: Apples and oranges

Just to clear this up I`m not saying or recomending any one to pull there cars apart and fit larger valves, on its own you may well see an extra 5 bhp. If you had to replace the head i think you would be silly not to replace it with the bigger valve head. If you are modifying a m30 motor to any degree the valves/cam timing would proberbly be the most obvious place to start, followed with porting, then maybe forged pistons and rods topped of with a race tec ecu/ignition controler ect ect. From my exsperiance in building up engines for a number of cars including Forced induction, valves are always the stumbling block and (cubic capacity and Turbos aside)govern the ultamate Hp a engine can produce. The first thing for me that govens the time when I decide you can longer get any more power out of a non-turbo engine no mater what you do is breathing thats is ultamatly dictated by valve size.
very sorry if theres some spelling mistakes in there but i was under the impreshion this was a car site not a English litrature forum. My spelling has always and always will be bad and I asure you it not through lack of Education or stupidity.
Best regards
marc

They even went to the website and got his email

Re: "80" 633 E-24

Can anyone tell me if the newer "big valve" or standard valve 3.5 liter 6, will bolt into my car ? My 3.2 blew up and I want to upgrade, since the engine is coming out. Also, I was going to use my existing ECM and manifolds from the 3.2 liter engine. The car is a 1980 633CSi. thanks, Sean

Carl had done a friends 3.0 CS a few years ago

It's not that big a deal, when looking at both heads side by side, the B35 head is a more "open chamber" design, which would result in lower compression on an earlier engine. The intake ports are wider and the stock intake manifold barely seals on the sides. It produces a "step" going from the intake to the head, not a smooth transition. I am going to install an M90 (same bore and stroke as the M88/S38) in my '74 Euro 3.0CS. It is the engine used in the '79-'81 M535 and Euro '79-'81 635 and 735 - 218 HP. In california a '74 or earlier CS will not need to wory about smog issues, so I may upgrade with a Schneider cam, headers and B35 head with L-Jet manifold with motronic 1.1. A friend installed a new B35 that had been in his 633 into a '89 635 and he said the newer electronics "woke it up". The motronic bellhousings for the 265 trannys are very hard to come by, Carl just got one a week or 2 ago.